1. Field of the Invention
The present invention relates generally to vapor recovery systems and methods and, specifically, to a vapor recovery system for recovering vapors from a petroleum storage tank in order to deliver the vapors to a gas sales line.
2. Description of the Prior Art
In a typical petroleum production facility, the product from a producing well is first passed to an oil and gas separator, with the liquid petroleum being passed to a petroleum storage tank. The liquified portion of the tank contents are periodically emptied and transported.
While pentane and other heavier components of the tank contents are typically liquid, gaseous vapors develop in the upper portion of such tanks as the gases come out of solution in the process liquids. Vapor recovery units have been popular for a number of years. If the tank vapors are present in sufficient quantity to economically justify their recovery, it is often expedient to collect the tank vapors and compress the vapors to the point that they can be delivered to a gas sales line, where the vapor is sold in the gaseous state. Previously, if such sales lines were not present or if the gaseous vapor did not occur in sufficient quantity, the vapors were sometimes vented to the atmosphere or were burned in a flare.
The passage of the Clean Air Act, combined with more stringent enforcement of local air quality standards, have together obsoleted certain of the previous disposal methods. The newer air quality regulations increase the demand for systems that find ways to avoid disposing of storage tank vapors into the atmosphere either by direct venting or flaring. The more stringent emission control standards result in a need for disposal systems which have, in the past, been economically prohibitive. For many production operations, the difference between shutting down a well and keeping the well in production depends upon how economically the vapor emissions can be controlled.
The prior art vapor recovery methods have suffered from a number of deficiencies. Skid mounted gas collection and compression units require the use of a gas compressor which is relatively expensive to install and operate. Such units require a number of motors to operate and maintenance on the compressors is fairly high due to the abundance of mechanically moving parts, normal wear and tear, and the like.
It is an object of the present invention to provide an improved system and method for controlling tank vapors on a petroleum storage tank.
Another object of the invention is to provide a method for efficiently recovering tank vapors for sale which does not increase greatly the cost or complexity of the present operation.
Another object of the invention is to provide a non-electric recovery system which eliminates fire and explosion hazards.
Another object of the invention is to provide an improved vapor recovery system which meets the requirements of the Clean Air Act and which requires low capital expenditure and has low maintenance and operating cost.